有点复杂的题解

#include <bits/stdc++.h>
using namespace std;
int main(){
	string s, r = "";
	int st;
	cin >> s >> st;
	for(int i = 0; i < s.size(); i++) {
		int n = s[i] - 'A' + st;
		string t = "";
		while (n > 0) {
			t = char(n % 10 + '0') + t;
			n /= 10;
		}
		r += t;
	}
	while (r != "100" && r.size() > 2) {
		string t = "";
		for (int i = 0; i < r.size() - 1; i++) {
			int n = (r[i] - '0' + r[i+1] - '0') % 10;
			t += char(n + '0');
		}
		r = t;
	}
	while(r[0] == '0') r.erase(0, 1);
	cout << r;
	return 0;
}